The present invention relates to a pipe-cutting and/or welding machine with a pipe-turning arrangement, which has a chuck whose jaws are in contact with an activating device for the movement of the jaws.
Pipe-cutting machines serve for the preparation of pipe fitting sections; for the preparation of various types of cuts, a respective movement of the cutting torch as well as of the pipe to be cut being required. The movement of the cutting torch is usually undertaken by means of compound lever arrangements as taught for example by German Patent No. 937,387; 940,027 and 961,588.
For moving and stopping the pipe to be cut, the pipe in most instances is clamped in a pipe-turning arrangement by means of a chuck. For the moving of the chuck which clamps or releases the pipe, an activating device is provided having an electric motor with a clutch. The clutch is constructed here in such a manner that a predetermined factor it slips and consequently the clamping momentum, hence the force with which the chuck jaws are pressed against the pipe, is limited to a predetermined value. It has been shown in practice that by means of such an arrangement only a single constant tension value may be achieved, wherein the extent of the tension value must be designed in such a manner that both thick-walled as well as thin-walled pipes may be clamped firmly. The activating device was therefore designed for an average tension, which is sufficient for clamping thick and thin-walled pipes. In this connection, however, it has been shown that under certain circumstances the preselected tension with respect to thick-walled pipes, may lead to an insufficient grip, whereby relative movements between pipe and chuck may set in. On the other hand, with thin-walled pipes, the preselected tension may lead to a deforming of the pipe, something which is equally undesirable.
A further drawback of these known arrangements is that in many instances, upon the release, the forces transmitted from the activating device to the chuck jaws do not suffice to release the pipe. In most cases, the operator must proceed manually and remove the jaws from the pipe by externally exerted force on the chuck or chuck jaws. Even the introduction of a so-called impact clutch -- wherein a clutch half slips, by a defined measure, upon reaching a certain rotational speed and hits against a stop provided on the other clutch half -- indeed brings about an improvement with respect to the releasing of the chuck jaws but effects, on the other hand, very great mechanical strain on the entire clamping device, whereby its exactness and service life is considerably reduced.